During the deployment of a passive restraint device in the event of a collision involving a vehicle in which the device is installed, gases and particulate combustion products, produced at temperatures in excess of 1,000.degree. F. during the initial portion of the propellant burning cycle, impinge directly upon the fabric of the bag. If no protective measures are taken, such as: (1) by incorporating additional, i.e., "sacrificial", layers of fabric into the bag at the point where it is contacted by the hot gases and the energetic particulates, or (2) by installing a deflection member between the generator and the air bag, this impingement may result in the bag becoming burned through, with a resultant failure of the restraining device to perform as desired.
Manufacturers of currently marketed air bag systems have generally elected to do both, i.e., by providing a sacrificial layer and a gas deflection member. The deflection members in current use, however, are expensive, machined parts which are fabricated from heavy steel plate and which can not be stamped with conventional stamping equipment. This adds both to the cost of the inflator and the weight of the completed assembly. As is well known in the automotive art, any increase in vehicle weight is to be avoided if possible due to its negative impact upon gas mileage. The main function of these machined members appears more directed to simply attaching an air bag to a gas generator rather than to deflecting hot gases and particulates away from the fabric of the bag since they do not extend any appreciable distance into the mouth of the bag.
Further, with regard to the means for inflating air bag systems such as those described herein, many forms of gas generators or inflators utilizing combustible solid fuel gas generating compositions are known. Commonly encountered features among generators utilized for this purpose are the inclusion within a housing of a gas generant composition and means to filter and to cool the gas, positioned between the composition and the gas discharge orifices, as defined by the generator housing.
One such gas generator includes an annular reaction or combustion chamber which is bounded by an outer casing or housing structure. The combustion chamber encloses a rupturable container or cartridge that is hermetically sealed and which contains therein a solid gas generant in pelletized form, surrounded by an annular filter. This generator further includes a central ignition or initiator tube and a toroidal filter chamber adjoining and encircling the combustion chamber. An inner casing or housing structure is located in close surrounding and supporting relationship to the rupturable container, the inner casing being formed by a cylinder having uniformly spaced peripheral ports or orifices near one end. These orifices provide exit holes for the flow of gas from the combustion chamber.
Alternately, a generator housing may be provided, comprising first and second structural components or shells, specifically, a first or diffuser shell and a second or base shell. Both shells are forged and heat treated, after which they undergo machining to obtain a proper fit. The first structural component, i.e., the diffuser shell, is formed with three integral concentric cylinders which form the inner structural walls of the inflator and which define chambers therein containing the solid gas generant, ignition materials, and filters, as well as providing exit openings or ports for the passage of the gasses from chamber to chamber and subsequently into the protective air bag.
The second structural component of this embodiment, known as the base shell, may utilize an electrical initiator (squib) for igniting the main propellant charge as well as a flange for attaching an air bag thereto. It also provides three concentric mating surfaces for the concentric cylinders of the diffuser shell. The three concentric cylinders of the diffuser shell are thus joined to the corresponding concentric mating surfaces located upon the base shell.
Still further, other inflator devices which are known in the art comprise a base plate and a diffuser plate having a peripheral portion thereof sealingly connected to a corresponding portion of the base plate. This connection is made by, for example, a light weld between these two parts. The subject inflator additionally comprises means for engaging the base plate and the diffuser plate in operative association. These means pass substantially perpendicularly through both said plates and are preferably rivets, although bolts or screws may also be utilized for this purposes. Such engaging means are capable of permitting a minimal degree of separation between the diffuser plate and the base plate of the inflator in the event that the generator unit becomes overpressurized. This arrangement permits the rapidly generated gaseous product to be safely directed away from the generator, thus preventing a catastrophic fragmentation of the generator housing.
Gas generators, or inflators, of the type described above, must withstand enormous thermal and mechanical stresses for a short period during the gas generation process. Thus, inflators that have been and are currently being used with automobile or other vehicle air bags have previously been fabricated using steel for the casing and other structural housing components, with these components being joined together by screw threads, roll crimping or welding.
The recent emphasis on weight reduction for the purpose of fuel conservation in motorized vehicles, however, has created a need and a demand for a lighter weight inflation system. This is of particular importance in a crash protection system for the driver wherein the inflator is mounted on the vehicle's steering wheel. The availability of a lighter weight inflator for installation at this location further enables a reduction to be made in the weight of the vehicle's steering wheel and the steering column on which the inflator is mounted.
In this regard, some recently introduced inflator devices utilize aluminum casing materials. While this does alleviate somewhat the problem of excessive generator weight, aluminum generators tend to be more expensive in terms of production costs than the stamped stainless steel models currently in general use. More importantly, however, aluminum also tends to lose considerable strength at elevated temperatures, which becomes of concern should the airbag system be exposed to a car fire. Since the gas generator is a pressure vessel, as noted above, concern exists over the possible fragmentation of a weakened aluminum generator casing upon a sudden overpressurization of the device due to an ignition caused by such a fire.
Various means, as described above, have been utilized with the prior art inflators described herein to prevent the impingement of hot gasses and/or particulate materials directly upon the inner surface of an air bag installed in operative association therewith. Thus, as described below, the present invention describes and claims a novel deflector member configured and adapted to permit a safe, rapid inflation of an air bag component in a motor vehicle passive restraint device to assist in ensuring the safety of the vehicle occupants in the event of an accident.